ABO Exam Practice Test - Practice Exam & Study Guide for the American Board of Opticianry

When the pupillary distance (PD) is ground too narrowly for a minus prescription, it creates an imbalance resulting in the optical centers of the lenses being closer together than the patient's pupils. In this case, the light entering through the lenses is not aligned with the position of the eyes, leading to the need for prism correction.

For a minus prescription, the lenses are diverging, and if the PD is too narrow, it causes the eyes to converge more than necessary. This misalignment results in a base-in prism effect because the optical centers of the lenses are inward relative to the pupils. Therefore, the correct answer indicates that the prism base will be directed inward, compensating for the excessive convergence and helping to align the optical axis of the lenses with the visual axis of the eyes.

Understanding the effects of improper pupillary distance calibration in relation to minus prescriptions is essential, as it can significantly impact visual comfort and clarity.